circulatory system

[sûr′kyə-lə-tôr′ē]

The system that circulates blood through the body, consisting of the heart and blood vessels. In all vertebrates and certain invertebrates, the circulatory system is completely contained within a network of vessels (known as a closed circulatory system). In arthropods and many other invertebrates, a substance analogous to blood (known as hemolymph) is pumped through vessels that open into the intercellular spaces (in what is known as an open circulatory system). In vertebrates, the lymphatic system is also considered part of the circulatory system.

circulatory system

The system in the body by which blood and lymph are circulated. The parts of the circulatory system include the heart, along with all the arteries, veins, and capillaries. The organs of the lymphatic system are also considered to be part of the circulatory system. Nutrients, oxygen, and other vital substances are carried throughout the body by the blood, which is pumped by rhythmic contractions of the heart. Blood is pumped from the heart to the arteries, which branch into smaller and smaller vessels as they move away from the heart. The blood passes oxygen and nutrients to the cells and picks up waste in the capillaries, then returns to the heart via a system of veins.